Seven years is a long time for a story to last and, despite the fact that we’re dealing with a group of highly talented and well-trained witches and wizards, it affords ample opportunity for them to screw up.
We’ll kick things off with our titular protagonist, Harry Potter himself.
What is, we’d wager, took place in the preceding film, “Harry Potter and the Order of the Phoenix.” After dragging his friends to the Ministry of Magic’s Department of Mysteries — okay, they came willingly — intending to save his godfather, Sirius Black .
It’s not like Ron didn’t know his wand was busted; why would he attempt such a spell if he’d already experienced subpar results using it? We get that it could have just been a protective instinct to stick up for his friends, but if he’d have stopped to think, it would have saved him a trip to the Hogwarts infirmary and experiencing what we’d guess is a rather nasty aftertaste.
Of course, a mouthful of slugs is nothing in the grand scheme of things.
How about the time she made Polyjuice Potion in “Harry Potter and the Chamber of Secrets”? She, Harry Potter, and Ron Weasley intended to chat up Draco Malfoy while disguised as fellow Slytherin students Millicent Bulstrode .
Hermione’s biggest mistake, however, came in the form of a spell that was seemingly executed perfectly: hexing Cormac McLaggen’s , causing a rift over Hermione’s seemingly unrequited romantic feelings.
Oh, Neville Longbottom prophecy spoke of a boy born at the end of July, which also applied to Neville.
Neville’s biggest biff came during the Battle of Hogwarts during “Harry Potter and the Deathly Hallows: Part 2.” Having developed a penchant for disobedience when leading a rebellion at the school while Harry, Ron Weasley, and Hermione Granger were out hunting horcruxes, Neville goes a bit beyond the proverbial stiff upper lip; he gets cocky, as manifested in his decision to taunt the dark wizards that at temporarily held at bay by the protection spells cast over the school.
In throwing herself into the mix, while intending to help, she may have made things worse for Harry because now he has to worry about her safety in addition to his own; it wouldn’t exactly be a good look for him to rush out to fight two villains and end up losing his unofficial girlfriend who also happens to be his best friend’s sister.
When it comes to his mistakes, it would be easy to say “choosing to become a Death Eater,” but we’re not exactly sure he had much choice in the matter; he was being groomed for dark wizard glory from birth and this was pretty much a foregone conclusion.
Draco’s biggest mistake, if we’re playing devil’s advocate, was not giving Harry up to Bellatrix when the snatchers brought him, Ron, and Hermione to Malfoy Manor in “Deathly Hallows 1.” Harry himself even calls him out on it during the final film, saying Draco had to know it was him and asking why he didn’t say as much.
Professor Albus Percival Wulfric Brian Dumbledore .
We feel like falling in with the wrong crowd — read: Death Eaters — could be considered a pretty big whoopsie, though consider that Snape was bullied by the younger versions of the Marauders: James Potter .
But the book also contained a curse of Snape’s personal design — Sectumsempra — one which causes massive lacerations and hemorrhaging, bearing no warning or explanation of what it would do.
It’s tempting to joke that Moody accepting the job teaching Defense Against the Dark Arts at Hogwarts was his biggest mistake, but as a former auror, he spent his entire life putting himself in harm’s way as a force for good and, if he hadn’t been waylaid by Barty Crouch Jr.
Fortunately, when Remus Lupin came into possession of the Marauders’ Map — which he helped to create along with Sirius, James, and Peter — he knew Peter was still alive and was able to begin helping Sirius arrange for his capture.
They had Wormtail in custody, Harry had dealt with Snape, and everything was going swimmingly until Remus saw the full moon and went into full werewolf mode.
“Trying to kill Harry Potter as a teenager” is certainly a contender, considering doing so destroyed his seventh horcrux and made him that much more vulnerable — and forced him to make a guest appearance as a barbecued chicken drumstick in Harry’s mental train station.
We’ll never know because Voldemort’s insistence on killing Harry himself essentially caused his downfall and eventual death, owing to the fact that he was using the Elder Wand to battle the rightful wizard to wield it; Harry was as a result of disarming Draco Malfoy, who had similarly disarmed Professor Dumbledore to unwittingly become the wand’s rightful owner.